1. Field of the Invention
The present invention relates to a light beam scanner for deflecting a light beam with a light deflector, and more particularly to a light beam scanner for two-dimensionally scanning a fixed sheet with a light beam.
2. Description of the Prior Art
Light beam scanners including light deflectors such as galvanometer mirrors, rotating polygonal mirrors, and hologram scanners for deflecting a light beam to two-dimensionally scan a sheet have found wide use in various scanning recording apparatus, scanning readout apparatus, and the like. The two-dimensional scanning of the sheet has heretofore been effected by mechanically transferring the sheet in one direction for sub-scanning thereof while one-dimensionally deflecting the light beam in a direction substantially normal to the foregoing direction for main scanning of the sheet. For two-dimensionally scanning the sheet in this manner, it is important that the sheet being scanned be transferred at a stable speed in said one direction, i.e., the sub-scanning direction. If the sheet being scanned were not transferred highly accurately at a constant speed, it would be scanned irregularly by the light beam, and image information read out, for example, from the sheet during scanning thereof would be distorted. Therefore, the sheet has conventionally been transferred in the sub-scanning direction by a high-precision motor which can feed the sheet highly accurately at a low speed in one direction. However, since such a high-precision motor is expensive, the cost of the entire light beam scanner is substantially increased. Some sheets to be scanned by a light beam tend to flex out of complete flatness while they are being transferred. To allow such sheets to be transferred completely flatwise, it has been one practice to employ an attracting means such as a suction box within an endless belt which supports a sheet thereon and to activate the attracting means for holding the sheet in intimate contact with the endless belt to keep the sheet flatwise against accidental displacement while being transferred accurately at a constant speed. Use of such an attracting means in addition to the high-precision motor has resulted in a further increase in the cost of manufacture of the light beam scanner.
The space provided for the transfer of a sheet in the light beam scanner has to be of a size in the sub-scanning direction which is at least twice the length of the scanned area of the sheet in the sub-scanning direction. As a consequence, it has been difficult to reduce the size of the light beam scanner, and the relatively large light beam scanner is not suitable for use in a limited space.